Coorected bug. Added test case

.gitattributes

 *.dat filter=lfs diff=lfs merge=lfs -text
+*.vtk filter=lfs diff=lfs merge=lfs -text
+*.vtu filter=lfs diff=lfs merge=lfs -text

flutter/aero.py

@@ -86,8 +86,8 @@ class Aero:
         nf = 2 * self.nh + 1 # number of flow modes
         harmonics = np.zeros(nf) # sequence of harmonic factors (3 modes: [0, 1, -1])
         for i in range(self.nh):
-            harmonics[2*(i+1)-1] = 1 / (i+1)
-            harmonics[2*(i+1)] = -1 / (i+1)
+            harmonics[2*(i+1)-1] = i+1
+            harmonics[2*(i+1)] = -(i+1)
         instances = 2 * np.pi * np.arange(0, nf, 1) / nf # sequence of instances (3 modes: 2pi/N*[0, 1, 2])
         dft = 1 / nf * np.exp(-1j * np.outer(harmonics, instances)) # DFT[k,n] = 1/N * exp(-j*2pi/N*k*n)
         # Read the aerodynamic grid

tests/agard.py

+#!/usr/bin/env python3
+# -*- coding: utf8 -*-
+# test encoding: à-é-è-ô-ï-€
+
+# Copyright 2021 University of Liège
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os.path
+import numpy as np
+from iops import asciireader as ardr
+from iops import vtkreader as vrdr
+from iops import asciiwriter as awrt
+from flutter import pk
+from flutter import unmatchedfluid as flu
+from flutter import structural as sa
+from flutter import aero as aa
+from utils import testing as tst
+
+def main():
+    """3D Agard445.6
+       from Hüseyin Güner thesis, chapter 5, pp87 (http://hdl.handle.net/2268/245578)
+    """
+    # Geometric and structural parameters
+    ndim = 3 # dimension
+    c = 0.470 # aerodynamic chord
+    cr = 0.559 # root chord
+    mu = 68.8 # mass ratio
+    nmodes = 4 # number of structural modes
+    omegan = 2 * np.pi * np.array([9.5444, 40.3511, 50.2203, 97.6740]) # wind-off natural angular frequencies
+    amp = np.ones(nmodes) # amplitude of modes
+    pf = [-1, -1, -1, 1]; # modal participation factor
+    # Flight and flutter parameters
+    rho = 0.2082 # density
+    machs = [0.678] # Mach numbers
+    krefs = [0.05, 0.2] # reference reduced frequencies
+    ui = np.arange(0.2, 0.51, 0.01) # speed index
+
+    # I/O
+    matreadr = ardr.AsciiReader(os.path.join(os.path.dirname(__file__), 'data', os.path.basename(__file__)[:-3], 'structural')) # matrices
+    modreadr = vrdr.VtkReader(os.path.join(os.path.dirname(__file__), 'data', os.path.basename(__file__)[:-3], 'structural'), 'vtk') # modes
+    prsreadr = vrdr.VtkReader(os.path.join(os.path.dirname(__file__), 'data', os.path.basename(__file__)[:-3], 'aero'), 'vtu') # pressure
+    writer = awrt.AsciiWriter()
+
+    # Structural model
+    struct = sa.Structural(nmodes, 0.5*c, omegan, amp, pf)
+    struct.readMatrices(matreadr) # mass and stiffness matrices
+    struct.readModes(modreadr, 'dZ') # vertical modal displacement
+
+    # Aerodynamic model
+    fluid = flu.UnmatchedFluid(rho, ui, 0.5*cr, struct.omega[1], mu) # density and airspeed
+    aero = aa.Aero(machs, krefs)
+    aero.fromTime(prsreadr, 'Pressure_Coefficient', ndim, struct) # modal loads matrix from time instances
+
+    # Flutter solution using p-k method
+    sol = pk.Pk(struct, aero, fluid)
+    sol.run() # compute frequencies and damping and find flutter speed
+    sol.write(writer) # save to disk
+    if parse().fig:
+        sol.plot() # display results
+
+    # Testing
+    tests = tst.Tests()
+    tests.add(tst.Test('Flutter speed index (Mach 0.678)', ui[sol.fidx[0]], 0.38, 1e-2))
+    tests.run()
+
+if __name__ == "__main__":
+    main()